Microbiologically influenced corrosion (mic) or biological corrosion

one type of corrosion

1. microbiologically influenced corrosion (MIC) Presented by Nikhil Koshy Jacob ME – Industrial Metallurgy 14MY33 1

2. introduction Corrosion which takes place with the participation of some special kinds of microorganism on a metal surface is called microbiologically influenced (induced) corrosion (MIC ) MIC occurs on a metal surface in the presence of a suitable environment and conditions which help special kinds of microorganisms to participate in corrosion 2

3. The bottom of a crude oil storage tank after a microbial attack 3

4. Existence of Microorganisms The various microorganisms include bacteria, fungus, algae etc Estimation of bacteria quantity on the Earth gives a value of 5 million trillion of trillion (5 with 30 zeroes ) Today we are familiar with various microorganisms which live and grow in the environment at pH = 0 to 13, at temperatures between − 15to + 150◦ C , at pressures up to 1,000 bar, in aqueous solutions with different salt content (from pure water to the Dead Sea – 26% of salts), in oils, in fuels etc 4

5. Structure of a bacterium A rigid cell wall completely surrounds the bacterium and lies outside the membrane. Flagellum is a long filamentous appendage that propels bacteria. Pili are thin protein tubes. All bacteria need nutrients – the substances that bacteria consume for their existence, growth, and reproduction. These nutrients are carbon, nitrogen, sulphur , phosphorous, inorganic salts, and trace metals. 5

6. Structure of a bacterium 6

7. Motile bacteria can swim along a chemical concentration gradient towards a higher concentration of a nutrient, and this movement is called chemotaxis. Bacteria usually reproduce through binary fission, budding, chains of spores, and through the segmentation of elementary units, shortly, in asexual processes, in periods lower than 20 minutes. A single cell and its descendants will grow exponentially to more than 2 million cells in 8 hours 7

8. Classification of micro organisms Usually they are classified into three groups: aerobic, anaerobic, and heterotrophic Aerobic microorganisms use oxygen in metabolic processes . Anaerobic microorganisms grow in the environment without oxygen Heterotrophic microorganisms are those which can exist and grow both with and without oxygen 8

9. Mechanism of corrosion Here is a scenario how three major kinds of microorganisms capture the surface of metal. Probably , the trace of organic compounds and other nutrients are the first substances adsorbing on the metal surface and form “conditioning layer” for the attachment of microorganisms. The heterotrophic microorganisms usually settle on the first. Some of these cells adsorb to the surface for a finite time, and then desorb . This is called reversible adsorption. Some of the adsorbed cells form dense formation and become irreversibly adsorbed. There is no or only a low oxygen concentration underneath. Conditions without oxygen are convenient for the growth of anaerobic microorganisms under heterotrophic ones. 9

10. Aerobic microorganisms settle above heterotrophic ones and are close to the media (water, crude oil, fuel, etc.). Thus , anaerobic microorganisms are arranged the closest to a metal surface. Certainly , aerobic and heterotrophic microorganisms can separately settle on a metallic surface, form biofilm, and play, in this particular case, an essential role in the corrosion of metals. The development of a mature biofilm may take several hours to several weeks, depending on the system 10

11. Biofilm containing anaerobic, heterotrophic, and aerobic microorganisms 11

12. A large quantity of microorganisms form bio fouling(biofilm)defined with the naked eye and they are slippery to the touch. They choose metal surfaces as a place to live and form biofilm with thicknesses from several microns to several centimeters. Biofilm consists of microorganisms and substances (mainly products) of their metabolism. The latter is the sum of chemical reactions that take place within each cell of a living organism and that provide energy for vital processes and for synthesizing new organic material. Bacteria in biofilm excrete extracellular polymeric substances(EPS ), or sticky polymers, which work as glue and hold the biofilm together and cement it to the metal surface. BIO FOULING (BIOFILM) 12

13. EPS is called glycocalyx, which serves for trapping and concentrating nutrients from the water, and acts as a protective coating for the attached cells. Because the glycocalyx matrix holds a lot of water, a biofilm-covered metal surface is gelatinous and slippery. More than 99% of all microorganisms live in biofilm communities. Microorganisms adhere to carbon steels, stainless steels, and polymers (Teflon, PVC ) with almost equal “enthusiasm” within 30 seconds of exposure 13

14. Bio fouling in carbon steel pipes 14

15. Classification of corrosive microorganisms It is convenient to divide all microorganisms taking part or influence corrosion into five groups: Sulphate Reducing Bacteria(SRB). They are anaerobic and play an important role in corrosion of metals . Microorganisms producing acids . Microorganisms which oxidize ferrous (Fe2 +) and manganese ( Mn 2+) cations. Slime-forming bacteria. Methane (methanogens) and hydrogen producing bacteria . 15

16. Microorganisms causing corrosion SRB Desulphotomaculum Desulphovibrio vulgaris Microorganisms producing acids Thiobacillus Thiooxidans Bacteria oxidizing cations Fe2+( iron bacteria) and Mn2+ Galionella,Sphaerotilus 16

17. Prevention of MIC Changes of conditions in the system Aeration , if anaerobic bacteria are responsible for MIC, or agitation in order to prevent stagnation conditions. Mechanical scrubbing or scraping, and high-pressure spraying are also used Use of coatings Anti-fouling coatings of two types are mainly used. The first one contains biocides [ sodium hypochlorite (NaOCl), calcium hypochlorite{ Ca ( ClO ) 2 }, chlorine dioxide (ClO 2 )] which are released during the lifetime of the coating and which discourage the settlement and growth of microorganisms. The second type presents a sufficiently smooth surface to which microorganisms cannot attach. 17

18. Boiling of water It is one of the ancient disinfection measures. Many bacteria may be killed at 100 ◦C Use of ultraviolet (UV) light The rays from the sun contain the UV spectrum used in UV water treatment against microorganisms . In order to kill microorganisms, the UV rays must strike the cell and the energy penetrates the outer cell membrane, passes through the cell body, and disrupts its nucleic acids , thus preventing reproduction. 18

19. Use of ultrasound It consist of two mechanisms . The first mechanism produces conditions of cavitation ( hammer of water), which causes cell walls to break resulting in cell death. Cavitation is the process of formation and collapsing of Bubbles. The second mechanism is based on the apoptosis, or “dance of death”. As soon as the cells are exposed to the ultrasonic waves, they loose their ability to reproduce and will slowly enter into a dying phase. In other words, the ultrasonic waves induce microorganisms to commit suicide through a cascade of biochemical, physiological and morphological changes in the cell with membrane rupture 19

20. Reference 20

21. THANK YOU 21